Fisiología En Ac

Physiology of Ca Treated Produce
A.A. Kader Department of Pomology University of California One Shields Ave. Davis, CA 95616, USA Keywords: composition, ethylene, physiological disorders, quality, respiration Abstract Storage of fresh horticultural perishables within the optimum range of low oxygen and/or elevated carbon dioxide atmospheres for each commodity reduces their respiration andethylene production rates. However, outside this range respiration and ethylene production rates can be stimulated indicating a stress response, which can contribute to incidence of physiological disorders and increased susceptibility to decay. Exposure to 30-80 kPa oxygen atmospheres stimulates respiration and ethylene production and action in some commodities. Carbon dioxide-enriched atmospheresinhibit activity of ACC synthase, while ACC oxidase activity is stimulated by low carbon dioxide and inhibited at high carbon dioxide and/or low oxygen concentrations. Ethylene action is inhibited by elevated carbon dioxide atmospheres. Optimum CA retard loss of chlorophyll, biosynthesis of carotenoids and anthocyanins, and biosynthesis and oxidation of phenolic compounds. CA reduce the activity ofcell wall degrading enzymes that cause fruit softening and enzymes involved in lignification leading to toughening of vegetables. CA influence flavor quality by reducing loss of acidity, starch to sugar conversion, and biosynthesis of aroma volatiles, especially esters. Retention of ascorbic acid and other vitamins results in better nutritional quality, including antioxidant activity, of fruits andvegetables when kept in their optimum CA. INTRODUCTION Exposure of fresh fruits and vegetables to low O2 and /or elevated CO2 atmospheres within the range tolerated by each commodity reduces their respiration and ethylene production rate; however, outside this range respiration and ethylene production rates can be stimulated indicating a stress response. This stress can contribute to incidence ofphysiological disorders and increased susceptibility to decay. Elevated CO2-induced stresses are additive to, and sometimes synergistic with, stresses caused by low O2 levels, physical or chemical injuries, and exposure to temperatures, relative humidities, and/or ethylene concentrations outside the optimum range for the commodity. An overview of the general effects of elevated CO2 and reduced O2concentrations on causes of deterioration of fresh horticultural perishables is presented in Table 1. Specific concentrations of O2 and CO2 at which these general responses occur and their magnitude vary among commodities and cultivars, maturity and ripeness stages, storage temperatures and durations, and in some cases ethylene concentrations. RESPIRATORY METABOLISM The shift from aerobic toanaerobic respiration depends on fruit maturity and ripeness stage (gas diffusion characteristics), temperature, and duration of exposure to stress-inducing concentrations of O2 and/or CO2. Up to a point, fruits and vegetables are able to recover from the detrimental effects of low O2 and/or high CO2 stresses (fermentative metabolism) and resume normal respiratory metabolism. Plant tissues have thecapacity for recovery from the stresses caused by brief exposures to fungistatic atmospheres (>10 kPa CO2) or insecticidal atmospheres (40 to 80 kPa CO2). Postclimacteric fruits are less tolerant to CA stress and have lower capacity for recovery following exposure to reduced O2 and/or elevated CO2 levels than preclimacteric fruits. The speed and extent of recovery depend upon duration and levels ofProc. 8th Int. CA Conference Eds. J. Oosterhaven & H.W. Peppelenbos Acta Hort 600, ISHS 2003

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stresses, and underlying, metabolically driven cellular repair. Severe stress CA conditions decrease cytoplasmic pH and ATP levels, and reduce pyruvate dehydrogenase activity while pyruvate decarboxylase, alcohol dehydrogenase, and lacate dehydrogenase are induced or activated. This causes...